A conventional electrical switching apparatus in one form typically comprises an electromagnetically actuated device having a magnetic core proximate an armature. Typically, a coil is electrically energized to draw the armature to the magnetic core. The electromagnetically actuated device may be a control relay, a contactor, a motor starter or the like. The armature is operatively associated with a movable device such as an actuator. With an electrical switching apparatus the actuator operates a contact assembly.
A contact assembly may be an integral component of the electrical switching apparatus or it may be an auxiliary device to be added thereto. In either case, the contact assembly typically includes a contact having a pair of stationary contacts and a movable contact. In one known form of a contact assembly, a pusher is movably mounted in an enclosure. The stationary contacts are fixedly mounted in spaced relation with one another. The movable contact is mounted to the pusher. The contact assembly may provide for normally open contact operation or normally closed contact operation. In some conventional contact designs a different geometry stationary contact is used for normally open and normally closed stationary contacts. However, a problem exists in that a simple continuity test may not detect whether the incorrect stationary contacts are installed in such a design. Moreover, the movable contact may include silver contact points on one side of a conductive bar. A simple continuity test will not detect whether the movable contact is facing in the correct direction.
An additional problem of a conventional contact assembly is the improper installation of the pusher. If the pusher moves in a linear direction, and it is mistakenly mounted in an inverted position, then the movable contact will not line up properly with the stationary contacts. Some conventional designs use a small tab on the pusher received in a pocket in the enclosure. However, incorrect assembly may not be obvious during installation until after the cover and housing forming the enclosure are riveted together and the pusher binds during testing. At this point in the manufacturing process the problem is discovered, but the parts may not be salvageable.
Additionally, different variations of contact assemblies may require the availability of multiple pusher designs based on the location and orientation of the movable contacts. For example, both contacts can be normally opened, both contacts can be normally closed, one contact can be normally open and the other normally closed. Additionally, the timing of one contact opening and the other closing can also be altered. These variations necessitate additional parts inventory resulting in loss of economies of scale.
Accordingly, there is a need for a contact assembly for use in an electrical switching apparatus designed to eliminate opportunity of incorrect assembly.